The attack on olives by the pest Bactrocera oleae has been studied to determine its influence on the olive oil quality (free acidity, peroxide value, UV extinction, sensorial quality), the total polyphenol and the individual phenolic compounds. The Algerian chemlal olive variety was used in this work. Quantitative and qualitative analyses of phenolic compounds were performed using the colorimetric method and the GC coupled with mass spectrometry. The results demonstrated that the attack modified the quality of olive oil and confirmed the existence of hydrolytic and mostly oxidative processess which strongly reduced the amount of O-diphenolic compounds. The extent of modification was much greater when the olives were attacked and harvested at an advanced stage of maturity. Early harvesting could be an effective way to limit the damage caused by B. oleae and to improve the quality of virgin olive oil.